The strongest influence was Socioeconomic. Social needs and economic circumstance combined to influence the type and material of structures. Large halls were built not only when there was a societal need for them, but especially when the economic situat ion at that time permitted allocation of resources for such projects. One can see an example of this in the correlation between the two World Wars in Europe and the number of large public halls which were built. Both wars wrought destruction upon many c ities and the infrastructure of Europe. After hostilities ceased, a great percentage of the available capital was used for reconstruction related to the basic needs of the society: housing, roads, schools and factories. These were of the highest priority . There was little need for Market Halls when there was no way to transport products to a centralized location and even more fundamentally, there were very few goods to be sold at such a market. Swimming Halls were not required since there was little or no leisure time in which to go to a Swimming Hall. Furthermore, due to the reconstruction there was very little capital remaining for the erection of large halls. As basic needs were fulfilled, the planners moved on to larger structures, more far reachin g reconstruction, and restructuring of the cities.
Societal changes dictated a divergence in public construction. The industrialization in the second half of the 19th Century resulted in an explosive demand for cheap labor. This resulted in the rapid concentration of an equally rapidly increasing populat ion in cities. This massing generated the need for public bathing halls to ameliorate the cities serious hygienic problems. As toilets and other hygienic facilities were added to the standard features of the private realm, they were no longer required a s such in the public realm. This, coupled with an increase in personal leisure time, influenced the evolution of the utilitarian bath and shower hall to the sport swimming hall. This increased demand, coupled with the reduction of the cost of concrete c onstruction, resulted in a greater number of such halls being erected.
"Considering that only few years before that the erection of a swimming pool was considered a luxury, it is amazing to see that not only the largest of cities, but middle and smaller sized cities as well, can now count such a building to the inventory of public structures. This is the direct result of the expansion of reinforced concrete, which is not only good for the construction of the basins but for the columns, floors, roofs and cantilevered passages, making their erection simpler a nd reducing the costs."(8)The second major influence on the choice of structural form was Building Technology . This term is understood to include the entire realm of building (the verb) and construction technology. The development of these realms was dependent upon not only the structural designers, but on the contractors as well. The construction industry is traditionally conservative and slow to adapt. This was also the case when learning how to erect structures of reinforced concrete. Steel structures could be designed, pr e-fabricated and riveted together; reinforced concrete structures had to be first built of wood before concrete could be poured. This was an expensive process since most of the support scaffolding and formwork was often used only once. Traditional approa ches to construction were applied until newer, more rational methods specific to the new material were developed. New construction techniques, such as air-applied concrete, reusable forms and steel scaffolding, were invented or introduced to make the new material an economically viable option. Not only was the building process something new, but structural designers were unsure of how to properly design for the new material. Initially there was little understanding of how to calculate the internal force s or to design cross-sections of reinforced concrete elements. Structural theories had to be developed specific to this new combination of steel and concrete. The understanding of its physical properties grew slowly as they were experimentally determined . As the understanding of how to calculate the individual elements, structural systems and their interaction increased, the application of the material broadened. Simply understanding the concept of structural design was not enough, one had to be able t o build the structures.
The close relationship of the first two influences is described lucidly in an article in the Deutsche Bauzeitung in 1929. The article discussed(9) the design and construction of the newly completed m arket hall in Leipzig.
"The design and construction of the thin-shell is purely the result of the endeavor to open a way in which reinforced concrete could economically enclose large spaces. ... It is only with the development of the vaulted shell that it has b ecome possible to create column-free halls of great dimensions and to take advantage of the properties of a massive construction: a fire-proof and maintenance free structure."
Thus, one can see that the driving force of economics stoked the search for new building techniques for reinforced concrete.
The third major influence on the choice of structural form was Architectural Expression. This is understood to include not only the general architectural ideologies and "ideas of expression" which were prevalent at the appropriate historical mo ment, but also the architectural intent of the individual designers. There was a slow, but distinct, progression in the acceptance of reinforced concrete within the architectural community. First, it was scorned as not being worthy of consideration. It w as then embraced as the material to symbolize the new society which was to rise from the ashes of the first World War. This transition required not only the guiding vision of such architects as Perret and Garnier, but also the development of theories wi th allowed for, as well as propagated, the use of exposed concrete. It required the acceptance of the design profession to use reinforced concrete as a material in its own right; not as stone or a fluid material to be sculpted to any form. This theoreti cal development was in turn strongly influenced by the structural design of the large halls and the development of their specific language.